Heating element compartment for electric dryer applications

ABSTRACT

A heating box for an electric heating element is disposed in a clothes dryer. A substantially rectangular enclosure is opened at a first end and closed at a second end and internally supports one or more heating elements. A surface of the enclosure includes a plurality of holes which allow the heating element along its length to remain in contact with ambient air. The first end is connected to the heating duct of the dryer, and air enters through the plurality of holes and is heated. The air is drawn through the open end of the heating box due to a negative pressure applied to the dryer chamber into the dryer. In accordance with a preferred embodiment, the size of the holes changes along the length of the enclosure.

BACKGROUND OF THE INVENTION

The present invention relates to clothes dryers having electricalheating elements for generating drying air. Specifically, a heating boxis disclosed for an electric heating element assembly which increasesthe heat transfer efficiency of the heating element.

Both home and commercial clothes drying devices require substantial heatgeneration in order to provide drying air to remove moisture fromarticles being dried. Drying air is generated either from a gas burneror from an electrical heating element which operates from conventionalA/C. In the case of electric heating, drying air is supplied from aplurality of electrical elements which are connected to the electricalservice in the facility. A heating box surrounds the heating element,and ambient air enters one end and is drawn through to the second endinto a drying chamber of the dryer due to a negative pressure createdwithin the drying chamber from an impeller.

The life of the electric heating elements are finite, and, over time,replacement is necessary. The dryer down time as well as technicalsupport needed to replace the elements is a significant drawback forthis type of dryer which competes with the gas dryer.

It has been determined that the life expectancy of the electric heatingelements can be improved by improving the heat transfer rate from theheating element to the ambient air being heated for the dryer. As theefficiency goes up, the time of operation of the heating elementdecreases, prolonging the life of the heating elements. The presentinvention has been designed in an effort to improve the efficiency ofelectrically heating drying air and which will produce a longer usefullife for the heating element.

SUMMARY OF THE INVENTION

A heating box is provided by an enclosure which encloses a heatingelement and has an open end which supplies hot air to the dryer dryingchamber. Ambient air enters holes along the surface of the enclosure andis heated to a drying temperature. The holes in the surface of theenclosure have a diameter which varies over the length of the enclosure.Ambient air is in contact with the entire length of the heating elementcreating a more uniform transfer of heat from the heating element to theambient air.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a heating box in accordance with the presentinvention implemented in a commercial laundry dryer;

FIG. 1B is an isometric view of the laundry dryer of FIG. 1A;

FIG. 2 illustrates an exploded view of the heating box of FIG. 1;

FIG. 3 illustrates an isometric view of a heating box;

FIG. 4 is an end view showing connections to the heating elements in theheating box and the contactor;

FIG. 5 is a top view of another embodiment of the invention;

FIG. 6 is a front view of the embodiment of FIG. 5;

FIG. 7 is a bottom view of the heating box of the embodiment of FIGS. 5and 6; and

FIG. 8 illustrates the connection to the heating elements in the heatingbox.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIGS. 1A and 1B, a section view and isometric view of acommercial laundry dryer are shown. The laundry dryer includes a dryingdrum 12 supported for rotation on bearings 17. An opening 14 to thedrying drum 12 is closed by the door 15.

Drying air is provided to the drying drum 12 from a source of electricheating elements within a heating box 19 supported by bracket 21. Airwithin the heating box 19 enters through a plurality of opening 31 inthe surface of the heating box enclosure 19. Heating box 19 supplies hotair through a duct 20 into an opening of drying chamber 12.

The heating box of the preferred embodiment is disclosed moreparticularly in FIGS. 2, 3 and 4. The enclosure 25 is rectangular andincludes a plurality of holes 29, 31 on the top surface thereof as wellas 32 and 33 on the side surface thereof. The bottom 23 is shown havingno holes. An open end of the heating box includes tabs 26 which engage asurface of the dryer forming the heating duct 20, and the opposite endof the heating box 19 is closed. The holes along the surface of theheating box are evenly spaced and generally sized so that the holesdecrease in diameter as the distance from the closed end increases.Thus, the holes 29, 32 near the closed end of the heating box are sizedlarger than the holes 31, 33 at the open end of the heating box 19. Theeffect is to uniformly distribute ambient air entering through holes 29,31, 32 and 33 along the length of the heating element. The result isthat heat transfer from the surface of the heating elements is moreuniform than in the conventional arrangement where ambient air entersthrough an open, opposite end of a heating box having no holes along itslength. Contactor 24 supplies electrical current to each of the heatingelements 27.

In a typical configuration, the heating elements of the prior art woulddeliver a certain wattage of heat. In the preferred embodiment of thepresent invention, the element wattage rating can be increased and stillallow the same element operating temperatures. Instead of a higher heatoutput with the larger heat element, the temperature may be lowered foreach of the heating elements in order to preserve the life of theheating elements. For instance, a 100° decrease in temperature maydouble the element life.

A second embodiment of the invention is illustrated with respect toFIGS. 5-8. FIG. 5 represents a top view of a rectangular heating boxwhich includes holes 41, 42 extending across the top surface of theheating box. Holes 41 have a smaller diameter than those identified as42. Air flows into the holes 41 and 42 and out the exit opening in thebox 45 communicating with the hot air duct 20. The opposite end of thebox 49 is closed so that all air flow must be through holes in the top,sides and bottom of the heating box.

The side view of FIG. 5 is shown in FIG. 6, and includes a plurality ofterminals 47 which connect the electrical heating elements to acontactor 24 which supplies operating current to the heating elementsunder control of the dryer controller.

The side walls of the heating box include a plurality of channels 48which support the heating elements in a stacked arrangement with heatingbox 19. A heating box support 48 is shown to support the closed end ofthe heating box within the dryer.

FIG. 7 illustrates a bottom view, wherein a plurality of holes 43, 44are shown along the length of the heating box 19. As in the top surfaceof the heating box, the bottom surface includes smaller diameter holesat the open end exit 45 and larger holes 44 at the closed end of theheating box 49.

FIG. 8 illustrates terminals 47 which are connected to the heatingelements and to the contactor by wires (not shown). In the embodimentshown, it is contemplated that six heating elements would be provided,each pair of heating elements having a common terminal with theremaining end of the heating element connected to one phase of the threephase electrical system.

Using the principles of the foregoing embodiments, the heat distributionover the heat elements is distributed more uniformly, increasing thelife of the heating element.

The foregoing description of the invention illustrates and describes thepresent invention. Additionally, the disclosure shows and describes onlythe preferred embodiments of the invention in the context of a heatingelement compartment for electric dryer applications, but, as mentionedabove, it is to be understood that the invention is capable of use invarious other combinations, modifications, and environments and iscapable of changes or modifications within the scope of the inventiveconcept as expressed herein, commensurate with the above teachingsand/or the skill or knowledge of the relevant art. The embodimentsdescribed hereinabove are further intended to explain best modes knownof practicing the invention and to enable others skilled in the art toutilize the invention in such, or other, embodiments and with thevarious modifications required by the particular applications or uses ofthe invention. Accordingly, the description is not intended to limit theinvention to the form or application disclosed herein. Also, it isintended that the appended claims be construed to include alternativeembodiments.

1. A heating box for an electric heating element comprising: anenclosure open at a first end supporting a heating element and closed atan opposite end, a surface of said enclosure including a plurality ofholes which allow said heating element along its length to remain incontact with ambient air, said first end being open and arranged todeliver heated drying air to a drying chamber of a laundry dryer.
 2. Theheating box according to claim 1, wherein said holes are evenly spacedalong said enclosure surface.
 3. The heating box according to claim 2,wherein said holes vary in size from said closed end of said enclosureto the open end of said enclosure.
 4. The heating box according to claim1, wherein said heating box has a rectangular cross section.
 5. Theheating box according to claim 4, wherein each surface of said heatingbox includes said holes.
 6. The heating box according to claim 4,wherein said plurality of holes vary in size from said open end to saidclosed end with larger holes being located near said closed end.
 7. Amethod for equalizing the temperature distribution across a heatingelement comprising: supporting said beating element in an enclosure,said enclosure being open at one end arranged to deliver heated dryingair to a drying chamber of a laundry dryer and closed at an oppositeend; and locating holes along the length of said enclosure having a sizewhich varies from one end to another, whereby the heating element is incontact with the ambient air along substantially along its entirelength.
 8. The method for equalizing the temperature distribution acrossa heating element according to claim 7, wherein said holes adjacent anend which delivers hot air are smaller than the holes adjacent theclosed end.
 9. The method for equalizing the temperature distributionacross a heating element according to claim 8, wherein said holes aredistributed on each of four surfaces of a rectangular enclosure.